Electrodes on a mounting substrate and a liquid crystal display apparatus including same

ABSTRACT

An electrode wiring on a mounting substrate adapted for use in liquid crystal display apparatus, the electrode wiring including portions of Mo or Mo alloy to which bumps of an integrated circuit such as LSI is bonded with conductive paste.

This is a continuation of application Ser. No. 07/897,604 filed on Jun.10, 1992 which is a continuation of U.S. Ser. No. 07/594,301, filed Oct.9, 1990, both now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a wiring arrangement, andmore particularly to electrode wiring on a mounting substrate adaptedfor use in liquid crystal display apparatus, the electrode wiringincluding portions of Mo or Mo alloy to which bumps of an integratedcircuit such as an LSI are connected.

2. Description of the Prior Art

As a method of mounting an integrated circuit (IC) or the like on asubstrate, a direct bonding in which IC chips are connected face-down toa substrate is well known. In this method, tiny electrodes formed on theIC chips are connected to electrodes on the mounting substrate withconductive paste, etc. This method is particularly suitable when a largescale integration (LSI) with high integration is mounted on the mountingsubstrate.

For connection convenience, electrodes of ICs are projected, which arecommonly called bumps, and those projected on the mounting substrateconnected to the bumps are called pads because of their pad-like nature.A number of circuit pattern wirings are electrically connected to thepads on the mounting substrate.

Japanese Laid-Open Patent Publication No. 60-238817 discloses a methodof mounting ICs or the like for driving a liquid crystal by using aglass substrate of a liquid crystal panel as a mounting substrate in theabove-mentioned manner. This method makes possible a direct mounting ofan IC on the panel for driving a liquid crystal, an LSI, or the like,with the use of an increasing number of pins depending upon amagnification, a high definition, and a minimization of picture elementpitches of a liquid crystal display apparatus. This method uses padsmade of Au or ITO (Indium Tin Oxide).

However, the above-mentioned known method has the following problems:

When the pad is made of Au, the connection resistance at a connectingportion between the bumps and pads is low and stable. The formation ofsuch a pad requires a gilding process, thereby complicating the step. Inaddition, Au is expensive, and the production cost becomes high.

When the pads are made of ITO, it is advantageous in that the process ofmaking them can share the process of making transparent electrodes ofITO during the production of a liquid crystal display panel, therebyreducing the number of steps in the process. However, there is a problemthat the connection resistance at the connection points between the padmade of ITO and bumps becomes high (5-10Ω). When the connectionresistance increases, the voltage applied to the liquid crystal displayportion substantially decreases due to a voltage drop at the connectionpoints, so that the quality of the resulting display becomes poor. Thisis particularly notable in a large-sized or highly definitive liquidcrystal display apparatus. These display apparatus generate a number ofoutputs per IC so as to drive a liquid crystal with high clockfrequency, and a greater power consumption in the ICs and a liquidcrystal itself, so that instantaneous passage of a current is difficultthrough the circuit patterns. This causes a further drop of the voltageapplied to the liquid crystal display portion.

SUMMARY OF THE INVENTION

The electrode wiring of the present invention, which overcomes theabove-discussed and numerous other disadvantages and deficiencies of theprior art, comprises portions of Mo to which bumps of an integratedcircuit such as LSI are connected.

According to another aspect of the present invention, the electrodewiring comprises portions of Mo alloy to which bumps of an integratedcircuit such as LSI are connected.

In a preferred embodiment, the mounting substrate is the substrate of aliquid crystal display panel.

In a preferred embodiment, the portions of Mo or Mo alloy are connectedto the bumps of an integrated circuit through conductive paste.

Thus, the invention described herein makes possible the objectives of(1) providing an electrode wiring which can be connected to anintegrated circuit without the possibility of increasing connectionresistance at the connecting portions to the integrated circuit, and (2)providing an electrode wiring which can be connected to an integratedcircuit easily and economically.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention may be better understood and its numerous objects andadvantages will become apparent to those skilled in the art by referenceto the accompanying drawings as follows:.

FIG. 1 is a sectional view showing an example of the present invention;

FIGS. 2, 3, 4, and 5 are sectional views showing another examples,respectively; and

FIGS. 6, 7, 8 and 9 are sectional views showing modifications to theembodiments shown in FIGS. 1, 2, 3 and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a main portion of a liquid crystal display panel 20 onwhich electrodes pads 10 are formed. A liquid crystal 3 isliquid-tightly sandwiched between glass substrates 1 and 2 of the liquidcrystal display panel 20. On the glass substrate 1 is formed an inputcircuit pattern wiring 5 and output circuit pattern wiring 4respectively for a liquid crystal driving LSI 6. The input circuitpattern wiring 5 is connected to an outside control circuit (not shown).The output circuit pattern wiring 4 is connected to a wiring or anelectrode in a liquid crystal cell of a display portion of the liquidcrystal display panel 20. The circuit pattern wirings 4 and 5 can bemade of a transparent conductive film such as an ITO, Ni, Cu/Ni, Ti, Ta,W, or Al.

The pads 10 are disposed at predetermined positions on the circuitpattern wirings 4 and 5 so as to effect connection between the patternwirings 4, 5, and bumps 7 of the liquid crystal driving LSI 6. The pads10 are made of Mo.

The liquid crystal driving LSI 6 is connected to the Glass substrate 1of the liquid crystal panel 20 by a face-down bonding method. The bumps7 of the LSI 6 is connected to the pads 10, preferably, with conductivepaste 8, and is connected to the input circuit pattern wiring 5 and theoutput circuit pattern wiring 4 through the pads 10. The conductivepaste 8 of silver or any other conductive substance is applied at leastto the top ends of the bumps 7 by use of a dispenser or a transcriberbefore the LSI 6 is mounted on the Glass substrate 1. In order toprotect the pads 10 from being dissolved or eroded by a solvent or thelike used in subsequent processes after the LSIs 6 are mounted, theconductive paste 8 may completely cover the pads 10 as shown in FIGS. 1to 4, wherein the adjacent conductive pastes 8 are electricallydisconnected from each other as with the interposition of a knownelectrically insulating film which is omitted in FIGS. 1 to 4.Alternatively, the conductive paste 8 may only cover the top portions ofthe pads 10 as shown in FIGS. 6 to 9, that is, the adjacent conductivepastes 8 are arranged at intervals, thereby eliminating the necessity ofinterposing an electrically insulating films therebetween. The intervalbetween one pad 10 and the next is preferably 50 μm but it can be largerthan 50 μm, for example, 100 μm. Instead of silver, gold paste, copperpaste, or carbon paste as the conductive paste 8.

In order to prevent the erosion of the pads 10, an anti-moisture resin 9is filled in the spots between the LSI 6 and the glass substrate 1, andis allowed to harden.

As mentioned above, the pads 10 of Mo have the following advantages:

The pads 10 made of Mo are stable throughout the subsequent processes offorming the liquid crystal panel. For example, an insulating layerlikely to increase connection resistance is prevented from being formedon the surface of the pads 10 even if the subsequent process includes astep at which an oxiding reaction occurs. As a result, the connectionresistance at the connecting portions between the pads 10 and the bumps7 is kept constantly low. In the present example, the connectionresistance is several hundreds mΩ. In contrast, in the comparativeexample using pads made of either Ti, Ta, W, or A1 the connectionresistance between the pads 10 and the bumps 7 is several Ω to severalhundreds Ω. Ti, Ta, W, or A1 are metal materials whose specificresistances are as low as that of Mo but they are disadvantageous inthat they are likely to form an unnecessary insulating layer on thesurface of the pads owing to an oxidation reaction during the formationof the panel. In the comparative example, the connection resistance atthe connecting points with the bumps 7 is increased because of thepresence of this insulating layer.

In the illustrated embodiment the pads 10 are made of Mo, which is notliable to an oxidation reaction, and are bonded to the bumps 7 of the ICwith conductive paste 8, so that the connection resistance therebetweenis low. Thus, the voltage applied to the liquid crystal display portionis prevented from dropping. Also, the pads 10 covered by the conductivepaste 8 are protected against deterioration by a solvent in the courseof the subsequent process of forming the panel. As a result, whether itmay be a large-sized liquid crystal display apparatus or a highlydefinitive liquid crystal display apparatus, desired display conditionsand high yield are satisfied.

Mo is a relatively cheap material, thereby reducing the production cost.In addition, Mo is used to make wirings and electrodes in the displayportions of the liquid crystal display panel 20. Therefore, when thewirings and the electrodes are to be made of Mo, the pads 10 can be madein the same process. As a result, the step of forming the pads 10 isreduced, thereby saving time and money in production.

FIG. 2 shows another example. In this example, the wiring 12 made of Mois formed in one piece with the pad 10 on the circuit pattern wirings 4and 5. A current flows through the circuit pattern wirings 4 and 5 andthe wiring 12 at the same time, thereby reducing the wiring resistanceas a whole.

FIG. 3 shows a further example. In this example, the input circuitpattern wiring 15 and output circuit pattern wiring 14 are made of Mo inone piece with the pads 10 of Mo. The pads 10, the circuit patternwirings 14 and 15 are formed in a single process, thereby reducing theproduction steps.

FIG. 4 shows a still further example in which another wiring 13 made ofa conductive material other than Mo is mounted on the circuit patternwirings 14 and 15 of Mo shown in FIG. 3. The wiring 13 is situated atpositions other than those at which the bumps 7 of the LSI 6 areconnected to the circuit pattern wirings 14 and 15, and at thepredetermined position the pads 10 of Mo are bonded to the bumps 7 ofthe LSI 6 with conductive paste 8. The wiring resistance is reduced.

FIG. 5 shows another example in which a protective film 16 made of SiO₂,SiN or the like is formed on the circuit pattern wirings 4 and 5 toprotect against deterioration of the circuit pattern wirings 4 and 5 notonly during the formation of the panel but also after the panel isformed. Thus, the production yield and reliability of the liquid crystaldisplay apparatus is enhanced.

In the illustrated examples, the circuit pattern wirings 4 and 5 aremade in single layers of ITO, Ni, Cu/Ni, Ti, Ta, W, or Al. It is ofcourse possible to make the wirings in multi-layers. Experiments havedemonstrated that when the pads 10 are made of Mo alloy such as Mo--Si(molybdenum silicide), the same effects are obtainable.

The pads 10 are made of Mo in a single layer, but as long as theportions of the pads 10 bonded to the bumps 7 of the liquid crystaldriving LSI 6 are made of Mo or Mo alloy, the pads 10 can bemulti-layered if the top layers are made of Mo or Mo alloy.

The glass substrate 1 of the liquid crystal display panel 20 is used asa mounting substrate, but the material for the mounting substrates isnot limited to glass. Various materials can be used. Therefore, becauseof the adoption of a variety of material, the electrodes of the presentinvention are applicable to computers and any other electronicapparatus.

As is evident from the foregoing, the present invention reducesprocessing steps, thereby saving time and money of the production. Theconnection resistance at the connecting portions between the electrodeson the mounting substrate and the bumps of the integrated circuitbecomes low, thereby preventing the voltage applied to drive the liquidcrystal from dropping.

Since the electrode wiring on the substrate of a liquid crystal displaypanel is connected to the bumps of an integrated circuit such as an LSIfor driving a liquid crystal through Mo or Mo alloy layers, theconnection resistance therebetween is advantageously reduced, therebypreventing the voltage applied to the liquid crystal display portionfrom ineffectively dropping. Because of this advantage, whether it maybe a large-sized liquid crystal display apparatus or a highly definitiveliquid crystal display apparatus, satisfactory display conditions andproduction yields can be obtained. Moreover, when wirings and electrodesare made of Mo or Mo alloy for the liquid crystal display portion, theproduction process is simplified with a reduced number of steps. Thisreduces the production cost.

It is understood that various other modifications will be apparent toand can be readily made by those skilled in the art without departingfrom the scope and spirit of this invention. Accordingly, it is notintended that the scope of the claims appended hereto be limited to thedescription as set forth herein, but rather that the claims be construedas encompassing all the features of patentable novelty that reside inthe present invention, including all features that would be treated asequivalents thereof by those skilled in the art to which this inventionpertains.

What is claimed is:
 1. An electrode wiring on a mounting substrateadapted for use in liquid crystal display apparatus, the electrodewiring comprising:pads of Mo to which bumps of an integrated circuit areconnected through conductive paste, said Mo pads being arranged atintervals; an input circuit pattern wiring and an output circuit patternwiring both of which are made of the same materials, and ananti-moisture resin filled in the spots between the integrated circuitand the substrate; wherein said input circuit pattern wiring and saidoutput circuit pattern wiring are made of Mo, and said Mo pads aredisposed on and formed integrally with said Mo input circuit patternwiring and said Mo output circuit pattern wiring; and wherein themounting substrate is a substrate of a liquid crystal display panel. 2.An electrode wiring on a mounting substrate adapted for use in a liquidcrystal display apparatus, the electrode wiring comprising:pads of Moalloy to which bumps of an integrated circuit are connected throughconductive paste, said Mo alloy pads being arranged at intervals; aninput circuit pattern wiring and an output circuit pattern wiring bothof which are made of the same materials; and an anti-moisture resinfilled in the spots between the LSI and the substrate, wherein saidinput circuit pattern wiring and said output circuit pattern wiring aremade of Mo alloy, and said Mo alloy pads are disposed on and formedintegrally with said Mo alloy input circuit pattern wiring and said Moalloy output circuit pattern wiring; wherein the mounting substrate is asubstrate of a liquid crystal display panel.